Tumor-associated macrophages (TAMs) inhibit anti-tumor immune responses through the release of humoral mediators such as cytokines, prostaglandins, growth factors and metalloproteases. TAMs can also protect tumors from immune recognition by hampering cell-mediated immune responses through the cell-surface expression of inhibitory molecules such as B7-H4 (Kryczek et al., 2006, J Exp Med 203(4):871-81). TAMs derive from resident macrophages or from monocytes recruited by the tumor microenvironment and polarized at the tumor site (Qia and Pollard, 2010, Cell 141(1):39-51; Allavena and Mantovani, 2012, Clin Exp Immunol 167(2):195-205). Tumor infiltration with TAMs has been associated with poor patient survival and higher microvessel density (Coffelt et al., 2009, Biochim Biophys Acta 1796(1):11-8). Targeting TAMs represents a promising strategy against cancer and several approaches have already been developed, including depletion with clodronate liposomes (Zeisberger et al., 2006, Br J Cancer 95(3):272-81); inhibition of tumor recruitment by targeting of CFSR-1 and CCL2 (Loberg et al., 2007, Cancer Res 67(19):9417-24); and “re-education” through activation, via CD40 with anti-CD40 mAbs (Beatty et al., 2011, Science 331(6024):1612-6) or via HRG plasma protein (Rolny et al., 2011, Cancer Cell 19(1):31-44) or mannose receptor (Dangaj et al., 2011, PLoS One 6(12):e28386).
B7-H4 or B7x/B7s is a member of the B7 superfamily and has recently identified as an inhibitory modulator of T-cell response (Sica et al., 2003, Immunity 18(6):849-61; Prasad et al., 2003, Immunity 18(6):863-73; Zang et al., 2003, Proc Natl Acad Sci USA, 100(18):10388-92). When present at the surface of antigen presenting cells, B7-H4 negatively regulates T cell activation, possibly through interaction with a ligand that remains to be identified (Kryczek et al., 2006, J Immunol 177(1):40-4). B7-H4 adenoviral overexpression in pancreatic islets protected mice from autoimmune diabetes maintaining peripheral tolerance (Wei et al., 2011, J Exp Med, 208(8):1683-94). Consistently with this observation, B7-H4 knock-out mice are more resistant to infection by Listeria monocytogenes than their wild type littermates due to a higher proliferation of neutrophils in peripheral organs (Zhu et al., 2009, Blood, 113(8):1759-67).
B7-H4 is widely expressed at the mRNA level, but its restricted pattern of protein expression in normal tissues suggests posttranscriptional regulation. B7-H4 expression in tumor tissues was observed in various types of human cancers such as breast (Tringler et al., 2005, Clin Cancer Res 11(5):1842-8), ovarian (Kryczek et al., 2006, J Exp Med 203(4):871-81), pancreatic, lung (Choi et al., 2003, J Immunol 171(9):4650-4; Sun et al., 2006, Lung Cancer 53(2):143-51) melanoma (Quandt et al., 2011, Clin Cancer Res 17(10):3100-11) and renal cell carcinoma (Jung et al., 2011, Korean J Urol 52(2):90-5; Krambeck et al., 2006, Proc Natl Acad Sci USA 103(27):10391-6). B7-H4 expression was evaluated by immunohistochemistry in most studies, either as a cytoplasm or a plasma membrane protein (Quandt et al., 2011, Clin Cancer Res 17(10):3100-11; Krambeck et al., 2006, Proc Natl Acad Sci USA 103(27):10391-6; Jiang et al., 2010, Cancer Immunol Immunother 59(11):1707-14; Zang et al., 2007, Proc Natl Acad Sci USA, 104(49):19458-63; Miyatake et al., 2007, Gynecol Oncol 106(1):119-27). In ovarian cancer cells, B7-H4 expression was assessed by flow cytometry and was also reported to be mainly intracellular (Kryczek et al., 2006, J Exp Med 203(4):871-81), to the exception of some cell lines where cell surface expression was observed (Choi et al., 2003, J Immunol 171(9):4650-4). B7-H4 has also been detected in a soluble form in blood samples from cancer patients (Simon et al., 2006, Cancer Res 66(3):1570-5; Thompson et al., 2008, Cancer Res 68(15):6054-8). The broad presence in various cancers of a negative regulator of T cell activation suggests a role of B7-H4 in down-regulating antitumor immunity. In fact, ovarian cancer-derived B7-H4+ TAMs suppress HER2 antigen-specific T-cell proliferation and cytotoxicity, and the blocking of B7-H4 expression on macrophages using morpholino antisense oligonucleotides in vitro and in vivo improves tumor-associated antigen T-cell responses (Kryczek et al., 2006, J Exp Med 203(4):871-81).
Altogether, these results support B7-H4 translational value as a target molecule for anti-tumor immunotherapy. However, the use of antisense nucleic acids remains limiting in clinics, in part because of a low stability in vivo due to serum inactivation, enzyme degradation, and innate immune activation, but also because of the lack of specific targeting and rapid elimination when oligonucleotides are delivered in a naked form (Zhang et al., 2012, Mol Ther 20(7):1298-304). Other means for blocking B7-H4 activity need to be developed for clinical applications. The present invention addresses this need.